PROJECT SUMMARY/ABSTRACT Untreated HIV-1 infection leads to immunodeficiency and subsequent death from opportunistic infections. Though effective therapies exist, none is curative; hence therapy must be administered indefinitely and adhered to rigorously. Poor adherence results in emergence of drug-resistant HIV-1 variants, viremia and disease. The viral capsid, which forms a shell encasing the viral genome, represents an attractive yet underexploited target for therapy. The capsid, an assembly of subunits of the highly conserved CA protein, interacts with multiple cell host factors whose roles in infection are not well understood. In early studies, my laboratory showed that the proper stability of the viral capsid is critical for HIV-1 infection. In recent collaborative studies with Itay Rousso, have revealed that HIV-1 capsid disassembly, or uncoating, can be studied in vitro by atomic force microscopy (AFM) using purified HIV-1 cores. Using AFM and cryoelectron tomography of cores, we propose to study the relationship of intrinsic capsid stability and capsid-binding host factors, to the process of capsid uncoating that occurs during reverse transcription. The work will also determine the role of a charged cluster in the capsid protein and will test the validity of a recently-described structure of the CA protein pentamer present within the capsid lattice. Collectively, the project will improve our understanding of the structure-function relationships in the viral capsid, thereby facilitating the design and mechanistic understanding of emerging antiviral compounds targeting the capsid.